The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Generally, a diesel engine shows merits on fuel consumption and output torque, but it shows drawbacks in exhaust gas. That is, although the diesel engine produces less carbon monoxide CO and hydrocarbon HC, it produces more nitrogen oxide (typically called NOx) and particulate matters because of its high temperature of the combustion chamber due to its high compression ratio.
Typically, particulate matters can be reduced by combustion control, however, we have discovered that there is a dilemma that an emission control scheme for reducing NOx may result in an increase of particulate matters, and an emission control scheme for reducing particulate matters may result in an increase of NOx, such that it is difficult to reduce both the NOx and particulate matters.
Usually, a diesel engine is provided with a diesel catalyzed particulate filter (CPF) for reducing the particulate matters.
The CPF collects the particulate matters exhausted by the engine, and when more than a predetermined amount of the particulate matters are collected, the CPF is regenerated by burning the particulate matters collected in the CPF by increasing the exhaust gas temperature by employing post-injection.
On the other hand, a diesel engine is typically provided with an exhaust gas temperature sensor that senses an exhaust gas temperature at an upstream side of a turbocharger, and such detection of the exhaust gas temperature is useful for preventing overheating of the turbocharger, for limiting the exhaust gas temperature, and for preventing overheating of the CPF.
In addition, a lambda sensor is typically provided at a downstream side of the turbocharger in order to measure an air/fuel ratio for the purpose of controlling EGR and adjusting fuel injection.
Thus, an engine control unit (ECU) controls the fuel injection and post-injection, based on the data obtained by the exhaust gas temperature sensor and the lambda sensor located at the upstream and downstream sides of the turbocharger.
In this case, an electrode to measure an oxygen concentration is provided inside the lambda sensor, however we have discovered that the electrode of the lambda sensor is poisoned by various factors (for example, a poison due to a siloxane). If the electrode of the lambda sensor is poisoned, a lambda signal output from the lambda sensor is deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the present disclosure and therefore it may contain information that is not already known to a person of ordinary skill in the art.